The present invention relates to a process for obtaining in high yield phosphoric esters having a perfluoro-polyoxyalkylene structure useful to give hydro- and oil-repellence in the treatment of various natural and artificial substrata, such as for example, ceramic, wood.
Specifically, the present invention relates to a process which allows to obtain phosphoric esters having a perfluoropolyoxyalkylene structure with high conversions and yields. Besides, the process of the invention allows to obtain, startting from the same precursor alcohol, phosphoric esters having a perfluoropolyoxyalkylene structure with a complete absence of triester groups and to modulate in a predetermined way the molar ratio between monoester and diester groups. Phosphoric esters are therefore obtained having a variable and controllable monoester/diester molar ratio starting from the same precursor alcohol.
It is known that the phosphoric esters of perfluoropolyethers are used to give hydro- and oil-repellence or easy stain removal to a wide range of natural and artificial substrata.
For the above mentioned applications, depending on the type of substratum, mixtures are required having a different content of phosphoric mono- and di-ester to obtain optimal results in connection with the desired effect. Therefore, from the industrial point of view, it would be desirable to have available a process which allows to modulate in a predetermined way the mono/diester composition of the phosphoric esters obtained from the phosphatization reaction.
Phosphoric esters deriving from monofunctional (per)fluoroalkyl alcohols are known in the prior art. These compounds must be phosphoric diesters to confer suitable hydro- and oil-repellence properties. However, the synthesis of diester phosphates in high yield is difficult and it unavoidably leads to a mixture containing significant amounts of triester as by-product. This is undesirable since the phosphoric triester shows adhesion problems to the substratum to which it is desired to confer hydro- and oil-repellence.
Alcoholic precursors have been synthesized having a perfluoroalkyl structure containing two monofunctional perfluorinated chains linked to a hydrogenated alkyl radical having an alcoholic function (di-Rf-alcohols wherein Rf is a perfluoroalkyl group) or two alcohol functions (di-Rf-diols) as described in U.S. Pat. Nos. 3,935,277 and 4,946,992. Said patents describe the synthesis of di-Rf-alcohols and of di-Rf-diols by reaction of Rf-ethylenthiols with halogenated alcohols and dials. Phosphoric esters of di-Rf-diols are described in U.S. Pat. Nos. 5,091,550 and 5,132,445. However the synthesis of the precursor alcohols requires many steps and expensive intermediates. The phosphoric esters obtained from said precursors are not easily available on the market.
To impart hydra- and oil-repellence properties to natural and artificial substrata, it is also known, as described in U.S. Pat. No. 3,492,374, the use of phosphates deriving from monofunctional alcohols having a perfluoropolyoxyalkylene structure, of general formula:
[XCF2CF2O(CFXCF2O)xCFXCH2O]2PO(OM)
wherein:
X is F or CF3; x is an integer in the range 1-8; M is a cation such as for example H+, a cation of alkaline metals or an optionally alkyl substituted ammonium ion.
In this patent it is suggested the use of said phosphoric diesters to give oil-repellent properties to various materials for example textile fibres, skin, paper, plastic material, wood, ceramic. However these compounds are not very stable to hydrolysis. Besides, the synthesis reaction is carried out by using POCl3 as phosphating agent: there are no high yields and phosphoric triesters with the above drawbacks are obtained.
The most used method in the prior art for preparing fluorinated phosphoric esters consists in the partial esterification of the phosphor oxychloride POCl3, with an alcohol and subsequent hydrolysis of the reaction intermediates. However this process leads to the formation of phosphoric triesters which give the above drawbacks. Besides, the esterification reaction of alcohols with POCl3 takes place in highly exothermic conditions and with development of hydrochloric acid wherefore severe control measures are required, as regards both the process safety and the material used in the plant construction.
Another phosphatization reaction known in the prior art is is the reaction between an alcohol and the phosphoric anhydride P2O5. However this reaction leads to the formation of mixtures of monoesters and diesters in a fixed and not variable ratio, once the starting alcohol has been defined. Therefore this process does not allow to control in a predetermined way the mono/diester composition of the phosphoric esters obtained from the reaction, starting from the same precursor alcohol. From the industrial point of view this is a drawback since mono- and diester mixtures cannot be obtained in a variable ratio starting from the same precursor alcohol.
The need was therefore felt to have available a process for obtaining phosphoric esters having a perfluoropolyoxyalkylene structure (PFPE), which allows to obtain a complete absence of triester groups and to modulate in a predetermined way the molar ratio between the monoester groups xe2x80x94P(O)(OH)2, and the diester groups  greater than PO(OH) present in the final product obtained by the reaction.
The Applicant has surprisingly found a process characterized by high yields and conversions to obtain phosphoric esters having a PFPE structure with the above properties.
An object of the present invention is therefore a process to obtain phosphoric mono- and diesters mixtures having the formula:
[Rfxe2x80x94CF2xe2x80x94(CH2)qxe2x80x94Z]wxe2x80x94P(O)(OH)3xe2x88x92wxe2x80x83xe2x80x83(I)
HOxe2x80x94[OH(O)Pxe2x80x94Zxe2x80x94(CH2)qCF2xe2x80x94Oxe2x80x94RfCF2xe2x80x94(CH2)qxe2x80x94Z]vxe2x80x94P(O)(OH)2xe2x80x83xe2x80x83(II)
wherein:
w=1-2
v=1-6, preferably 1-4;
q=is an integer from 1 to 20, preferably 1-5;
Z=O(C2H4O)pxe2x80x94, O(CH2)nxe2x80x94Oxe2x80x94, O(C3H6O)pxe2x80x94, S(C2H4O)pxe2x80x94, S(C3H6O)pxe2x80x94;
n=is an integer from 1 to 20, preferably 1-10;
p=is an integer from 1 to 5, preferably 1-3;
Rf represents a (per)fluoropolyether chain;
Rf in formula (I) is a monofunctional perfluoropolyether chain wherein the chain end group is selected from: CF3Oxe2x80x94, C2F5Oxe2x80x94, C3xe2x80x94F7Oxe2x80x94, Cl(C3F6O)xe2x80x94, H(C3F6O)xe2x80x94;
said process comprising the following steps:
a) a monofunctional alcohol having a perfluoropolyoxyalkylene structure of formula:
Rfxe2x80x94CF2xe2x80x94(CH2)qxe2x80x94ZHxe2x80x83xe2x80x83(IA)
xe2x80x83or
a xcex1,xcfx89-diol having a perfluoropolyoxyalkylene structure of formula:
HZxe2x80x94(CH2)qxe2x80x94CF2xe2x80x94Oxe2x80x94Rfxe2x80x94CF2xe2x80x94(CH2)qxe2x80x94ZHxe2x80x83xe2x80x83(IIA)
wherein Rf, Z and q have the above meanings, is added with an amount of water in the range 1-60% by moles, preferably 5%-40% by moles, with respect to the alcohol equivalents;
b) the reaction product obtained in step a) is reacted with phosphoric anhydride P2O5 added in a single portion or in more portions with a ratio between the alcohol equivalents and the moles of phosphoric anhydride in the range 1.5:1-4:1, preferably 2:1-3:1;
c) the compound obtained in step b) is hydrolysed by water or by a diluted solution of hydrochloric acid;
d) optionally the organic phase is separated by a solvent immiscible in water;
e) the product is recovered from the organic phase.
Generally, Rf has a number average molecular weight in the range 300-8,000, preferably 500 and 3,000 and comprises repeating units having at least one of the following structures, statistically placed along the chain:
(CFXO), (CF2CF2O), (CF2CF2CF2O), (CF2CF2CF2CF2O), (CR4R5CF2CF2O), (CF(CF3)CF2O), (CF2CF(CF3)O),
wherein
X=F, CF3;
R4 and R5, equal to or different from each other, are selected from H, Cl, or perfluoroalkyl having from 1 to 4 carbon atoms.
In particular, the perfluoropolyether chain Rf is selected from the following structures:
xe2x80x94(CF2O)axe2x80x94(CF2CF2O)bxe2x80x94xe2x80x83xe2x80x831)
with b/a in the range 0.3-10, extremes included;
xe2x80x94(C3F6O)rxe2x80x94(C2F4O)bxe2x80x94(CFLO)txe2x80x94xe2x80x83xe2x80x832)
with r/b=0.5-2 when b is different from 0,
(r+b)/t=10-30 when t is different from 0,
b and/or t can also be 0;
L is selected from F, CF3;
a, b, r, t are integers the sum of which is such that Rf has values of number average molecular weight Mn as indicated above.
xe2x80x94(C3F6O)xe2x80x94 can represent units of formula:
xe2x80x94(CF(CF3)CF2O)xe2x80x94
and/or
xe2x80x94(CF2xe2x80x94CF(CF3)O)xe2x80x94;
The alcoholic precursors of formula (IA) and (IIA) are obtainable by well known processes of the prior art. To obtain the (per)fluoropolyethers see for example the following patents: U.S. Pat. Nos. 3,665,041, 2,242,218, 3,715,378, 5,714,637 and EP 239,123. The functionalized fluoropolyethers having an hydroxyl termination (IA) and (IIA) are obtained for example according to EP 148,482, U.S. Pat. No. 3,810,874.
The phosphatization reaction (step b) to obtain the compounds of formula (I) and (II) is carried out at temperatures in the range 20xc2x0 C.-120xc2x0 C., preferably 40xc2x0 C.-100xc2x0 C. In this temperature range the ratio between monoester groups and diester groups obtained by the invention process is independent of the temperature itself. The rate of addition of the phosphoric anhydride is regulated so as to maintain the reaction temperature within the above limits.
The compound obtained in the phosphatization step b) is subsequently hydrolyzed (step c) and the organic phase is separated. Generally the hydrolysis is carried ou by adding water, or a solution of diluted hydrochloric acid to the reaction admixture, or alternatively by adding the reaction admixture to the aqueous phase.
Optionally the organic phase is separated (step d) in case by a suitable solvent immiscible in water such for example methylene chloride, ethyl acetate and others known in the prior art.
The compound is then isolated (step e) from the organic phase for example by the evaporation technique of the solvent.
By the process of the present invention phosphoric esters of formula (I) and (II) are obtained having a molar ratio between the monoester groups [xe2x80x94P(O)(OH)2] and diester groups [ greater than P(O)(OH)] [ greater than PO(OH)] predetermined in connection with the amount of water used in step a). Besides, it has been found that the in the process of the invention the variation of the average molecular weight of the starting alcohol does not affect the molar ratio obtained between monoester/diester groups.
The invention process leads to the obtainment of a hydrolytically stable compound. In fact, even carrying out the phosphatization reaction in the presence of water, a reaction conversion always higher than 98% is obtained.
The Applicant has surprisingly found that the use of the ethoxylated alcoholic precursors of formula (IA) and (IIA) gives the advantage to carry out the phosphatization reaction in the presence of water to obtain the desired ratios monoester/diester groups. Said result is surprising and unexpected since it was not expected this effect due to the presence of water on fluorinated products of perfluoropolyether type, which, as well known, are hydrophobic.
Tests carried out by the Applicant (see the comparative Examples) show that in the case of not ethoxylated alcoholic precursors (q=1, Z=xe2x80x94O, xe2x80x94S in formula IA and IIA), the reaction conversion is very low (lower than 10%), when the reaction is carried out in the presence of water. In absence of water the phosphatization reaction takes place with good yields, but it is not possible to control the final monoester/diester composition in the desired ratios.
The mixtures of phosphoric esters having a PFPE structure of formula (I) or (II) having a predetermined ratio of monoester/diester groups and complete absence of triester groups result new. In the case of phosphoric esters of formula (II) deriving from bifunctional alcohols, the molar ratio monoester/diester groups can range between 60/40 and 90/10. In the case of phosphoric esters of formula (I) deriving from monofunctional alcohols, the molar ratio monoester/diester groups can range between 70/30 and 85/15.
The mono/diester admixtures of the invention are obtainable with a predetermined ratio starting from the same precursor alcohol; or starting from alcohols having different molecular weight. The predetermined mono/diester ratio is in connection with the amount of water used in step a).
As said the admixtures of the invention combine good hydro- and oil-repellence properties.
Optionally the mixtures of phosphoric esters of formula (I) and (II) can be neutralized by bases to obtain the corresponding salts having formula:
[Rfxe2x80x94CF2xe2x80x94(CH2)qxe2x80x94Z]wxe2x80x94P(O)(Oxe2x88x92M)3xe2x88x92wxe2x80x83xe2x80x83(IB)
xe2x80x83Mxe2x88x92Oxe2x80x94[Mxe2x88x92O(O)Pxe2x80x94Zxe2x80x94(CH2)qxe2x80x94CF2xe2x80x94Oxe2x80x94Rfxe2x80x94CF2xe2x80x94(CH2)qxe2x80x94Zxe2x80x94]vxe2x80x94P(O)(Oxe2x88x92M)(Oxe2x88x92M)xe2x80x83xe2x80x83(IIB)
wherein M is equal to:
Li+, Na+, K+;
(NH3R)+, wherein R=H or linear or branched C1-C22 alkyl radical, preferably H; R can optionally contain xe2x80x94OH groups; xe2x80x94(NH2RRxe2x80x2)+, wherein R and Rxe2x80x2 are independently the one from the other linear or branched C1-C22 alkyl radicals; R and Rxe2x80x2 can optionally contain xe2x80x94OH groups or can be linked each other to form a cycle with the nitrogen atom, such as for example the morpholine group;
(NHRRxe2x80x2Rxe2x80x3)+, wherein R, Rxe2x80x2and Rxe2x80x3 are independently the one from the other linear or branched C1-C22 alkyl radicals; R, Rxe2x80x2and Rxe2x80x3 can optionally contain xe2x80x94OH groups or can be linked each other to form a cycle with the nitrogen atom, such as for example the morpholine group.
As said, the salts of formula (IB) and (IIB) are obtained by neutralization of the esters of formula (I) and (II) with bases, such as for example alkaline metal hydroxides or secondary or tertiary amines. Preferred examples of bases are: potassium hydroxyde, sodium hydroxide, ammonium hydroxide, primary, secondary or tertiary amines such as for example methyl amine, diethyl amine, triethylamine, ethanolamine, diethanolamine, triethanolamine, morpholine and others.
The stoichiometry of the neutralization reaction can be controlled so as to reach only the first equivalence point, corresponding to the neutralization of the protons of the  greater than P(O)(OH) groups and one of the two protons of the xe2x80x94P(O)(OH)2 groups. The first acid proton of the phosphate to be neutralized is that of a strong acid and, as a result, a salt is obtained which in water produces a solution or dispersion having pH of about 7. For the neutralization of the second proton of the xe2x80x94P(O)(OH)2 groups, it is instead necessary to reach a pH of about 10.
The phosphoric ester salts are particularly useful used in aqueous dispersions for the above mentioned hydro- and oil-repellence applications.